Boasting about one’s weaponry is nothing unusual in war, where there’s little way of confirming the veracity of the claim. In that, Syrian President Bashar Assad was following a long tradition of wartime leaders, when he told the Hizballah-backed Lebanese channel al-Manar last Thursday that he had sufficient stockpiles of Russian weapons to pose a threat to Israel, thanks to arms deals with Moscow that date to before the war erupted in February 2011. “The contracts have nothing to do with the crisis,” Assad said in the interview. “We have negotiated with them on different kinds of weapons for years, and Russia is committed to honoring these contracts.”

In fact, Assad’s boast might be more than bluster. While there’s no sign that Moscow has delivered the long-range S-300 missiles that Israel has vowed to take out in bombing strikes (Russian officials estimate their earliest delivery date for the S-300s is late this year), Assad already has several air-defense systems from Moscow in his quiver, according to analysts who monitor arms shipments. In interviews they say they watched a steep military ramp-up by Syria in the period running up to the start of the war more than two years ago. While they agree that the S-300s are more accurate and have greater range than Assad’s current weapons systems, they say the Syrian leader is far from powerless without them. “We have seen over the past few years Russia supplying several different air-defense systems,” says Pieter Wezeman, senior researcher in the arms-transfer program of the Stockholm International Peace Research Institute, which tracks weapons flows worldwide. “They [Syrian government] have really increased their capability. The missiles are both short and long range. If the S-300s do arrive, that would top it all off.”

Among the missiles already in place are two regiments of S-200 surface-to-air missiles, which have a range of about 150 miles, “with no less than 240 missiles ready to be fired in a matter of minutes,” says Igor Sutyagin, a Russian military scientist and senior researcher at the London think tank, Royal United Services Institute. Sutyagin, who was jailed in Russia on charges of spying for the U.S. and freed as part of a spy-prisoner swap in 2010, says Assad “has a lot” of air-defense systems acquired from Russia, including between 12 and 20 short-range missile systems called Pantsyr-S, which have a range of about 7.5 miles and which can be mounted on vehicles. Those were delivered to Syria about a year ago, in what he believes is the latest confirmed arms shipment from Moscow. In addition, Assad has 1,200 air-defense guns and between 4,000 and 8,000 Strela portable shoulder-fired missiles. “That IS the GREAT stockpile of Russian air defense weaponry!” Sutyagin said in an e-mail to TIME.

Since Syrian rebels have no airplanes for Syrian forces to shoot down, Assad’s impressive air-defense arsenal has little bearing on the grueling war that has ravaged large parts of the country and killed an estimated 90,000 Syrians. But the antiaircraft weapons would be crucial if the U.N. voted to impose a no-fly zone over Syria or if Israel expands its sporadic strikes on Syria into a sustained bombing campaign. At that point, the S-300 missiles, which have a longer range and greater accuracy than Assad’s current weaponry, could inflict bigger losses and strike deep into Israel in retaliation — hence, Israel’s fury over the arms deal. With the S-300s in place, says Wezeman, “If Israel starts an air campaign, they would maybe lose a few more planes than they have until now. It is not a system which cannot be destroyed, but it would be a bigger campaign,” he says.

For Western leaders weighing their military options against Assad, the crucial lessons are from Libya, where NATO launched a massive bombing campaign in March 2011, after the U.N. Security Council voted to stop Muammar Gaddafi’s forces from advancing on civilians in Benghazi. Within days of the first U.S. Tomahawk missiles hitting Libya, Gaddafi’s air-defense systems had been crippled, and his military planes had been smashed or grounded. That allowed the Libyan rebels to advance quickly across the huge terrain of eastern Libya, although it took five months longer for them to capture Tripoli and drive out Gaddafi.

Syria’s military arsenal presents the West with a far different calculus, in part explaining why no Western country has intervened militarily so far. While Gaddafi had huge stocks of weaponry, including Russian and Chinese antiaircraft missiles, much of it was discovered after Gaddafi was killed in October 2011, lying unused in warehouses. That suggested that the Libyan military did not know how to install the new weapon systems or had not had time to do so, according to military analysts. And Assad could also have learned some lessons from Gaddafi’s spectacular defeat. Gaddafi lacked long-range missiles capable of combating the high-altitude bombing strikes that NATO fighter jets conducted over Libya. “It’s against these types of operations that, for example, the S-300s or other SAMs [surface-to-air missiles] could be used with some efficiency,” Wezeman says. “In Libya the systems were old and out of date, and the Libyans did not really know how to operate them. It would be much more difficult for outsiders to intervene in Syria, in the way that took place in Libya.”